Background

Syphilis is a sexually transmitted disease caused by infection with Treponema pallidum, which is classified into four stages (primary, secondary, latent and tertiary). If the patients with primary syphilis do not receive treatment, the bacterium will spread through their bloodstream, and set the stage for secondary syphilis. Syphilis can cause a wide range of systemic manifestations, such as papular rash, malaise, weight loss, muscle aches, generalized lymphadenopathy and meningitis [1]. In Japan and other countries, the number of patients with syphilis is increasing year by year [2,3,4]. Recently, several dozen reports showed the pulmonary involvement in patients with secondary syphilis [5,6,7,8,9,10,11,12,13,14,15,16]; however, it is still undetermined how to obtain a desirable specimen for a diagnosis of the pulmonary involvement, and how to treat it if not cured.

Here, we report a rare case of a lung abscess caused by secondary syphilis, that was definitely diagnosed by polymerase chain reaction (PCR) tests from the transbronchial biopsy (TBB) specimen and followed by surgery.

Case presentation

A 34-year-old Japanese heterosexual man presented to our hospital with a 4 cm heterogeneous mass in the right lower lobe (Fig. 2). He had had a symptom of productive coughing, sore throat and nasal discharge for 5 days, but he had no fever and no dyspnea, and his general condition was good. He had a medical history of minimal lesion nephrotic syndrome and had received corticosteroid therapy until 4 months prior to his first visit to our institution. He was a current smoker (15 pack-years). He had had sexual intercourse with a woman other than his wife 4 months prior to his first visit. Physical examination revealed right inguinal nontender enlarged lymph nodes, and erythematous papular rash over the palms, soles and abdomen (Fig. 1). However, cervical and supraclavicular lymph nodes were not palpable, and he did not have abnormal neurologic findings.

Fig. 1
figure 1

Erythematous popular rash. a: Erythematous popular rash over the solesm, b: Erythematous popular rash over the abdomen

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C-reactive protein level was elevated at 1.02 mg/dL as shown in the laboratory tests (Table 1). The rapid plasma reagin (RPR) and Treponema pallidum hemagglutination test (TPHA) revealed titers 1:64 and 1:5,120, respectively, although Human immunodeficiency virus testing was negative. Chest X-ray (Fig. 2a) and computed tomography (Fig. 2b) revealed a single mass lesion (4 cm in size) in the right lower lobe, and enlarged lymph nodes (4.5 cm in size) in the right inguinal region.

Table 1 Laboratory findings on the first visit to our institution
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Fig. 2
figure 2

Images of the lung mass. a Chest X-ray on the first visit to our hospital. A mass lesion was shown in the right lower field (arrow), b Chest computed tomography on the first visit to our hospital. A single mass lesion (4 cm in size) was shown in the right lower lobe of the lung (arrow), c Fluorodeoxyglucose-positron emission tomography (FDG-PET) before the surgery, 4 months after the first visit. A single mass lesion was still remained in spite of the antibiotic treatment. It had abnormal uptake with a maximal standardized uptake value (SUV max) of 2.51 (arrow)

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Diagnosed as secondary syphilis, amoxycillin 1500 mg per day and probenecid 1000 mg per day were orally administered for 2 weeks. Subsequently, rash, inguinal lymph nodes and serological markers were improved (Fig. 3), however, the lung mass remained unchanged in size (Fig. 2c). TBB confirmed the pulmonary involvement of syphilis by PCR techniques (tpp47-, and polA-PCR) (Fig. 4), whereas malignancy and other possible infections such as bacteria and fungi were negative (Table 2). Five months after the first visit, right basal segmentectomy was performed to exclude other comorbid diseases, especially malignancy. The remained lung mass was an abscess and histological analysis showed the granuloma formation by epithelioid histiocytes and Langhans giant cells with necrosis (Fig. 5). The comprehensive PCR tests for multi-microbes were performed in the resected lung specimens, and no microbes were significantly positive (Table 2). Subsequently, penicillin G 2.4 million units per day was intravenously administered for 2 weeks, and the pulmonary involvement has resolved without relapse after 8 months follow-up.

Fig. 3
figure 3

Clinical course of the treatment. The induction of the oral antibiotics caused fever, headache and exacerbation of erythematous papular rash on the next day, which was considered as Jarisch-Herxheimer reaction. Treatment for 2 weeks improved the rash and serological data. However, the lung mass had not changed in size. Surgical resection was followed, and then, additional intravenous antibiotics for 2 weeks was administered. Abbreviation; rapid plasma reagin test: RPR; Treponema pallidum hemagglutination test: TPHA

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Fig. 4
figure 4

Electrophoresis of the amplified products from the lung mass with polymerase chain reaction (PCR) techniques. BAL was performed with 20 mL saline. The two types of gene fragments of Treponema pallidum (tpp47 and polA) acquired from bronchoalveolar lavage (BAL) and transbronchial biopsy (TBB) was amplified by PCR techniques. Both gene fragments were positive in samples from TBB, but not BAL

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Table 2 Microbiological analysis in specimens obtained by bronchofiberscopy and surgery
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Fig. 5
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Gross and microscopic pathology of lung specimens obtained by surgery a Gross pathology showed pus inside the lung abscess (arrow), b Microscopic pathology showed granuloma formation by epithelioid histiocytes and Langhans giant cells (arrow), in addition to necrosis (arrow-head). Original Magnification X100. Hematoxylin and eosin (HE) staining

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Discussion and conclusions

This is a rare case of a lung abscess caused by secondary syphilis, that was diagnosed by PCR techniques in TBB. The abscess was not improved by antibiotics and required surgery.

Coleman showed the criteria for the clinical diagnosis of secondary syphilis with pulmonary involvement in 1983 [5], and several dozen cases have been reported [6,7,8,9,10,11,12,13,14,15,16]. In some of them, PCR was used for the diagnosis of pulmonary involvement (Table 3) [13,14,15,16]. PCR is useful for the diagnosis of the infection of Treponema pallidum [18, 19], because it is difficult to directly visualize Treponema pallidum. In those reports, PCR was used in samples from TBB, bronchoalveolar lavage (BAL), bronchial aspirate, or computed tomography-guided percutaneous needle aspiration (CTNA) [13,14,15,16]. Thus far, only one case has been reported on lung abscess caused by secondary syphilis, that was diagnosed by PCR in CTNA [15]. In our case, the results of PCR in samples from TBB, but not BAL, was positive. For the detection of some infectious diseases, TBB or the combination of BAL and TBB was reported to be useful [20, 21]. Thus, it could be important to perform TBB to detect the pulmonary involvement by Treponema pallidum.

Table 3 Reported cases of secondary syphilis with pulmonary involvement which was diagnosed by PCR techniques
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The lung abscess was not improved by 2 weeks of oral antibiotics. It may be because penetration of antibiotics into the abscess was impaired. We treated the present case with amoxicillin and probenecid, because there is no insurance coverage for intramuscular penicillin for syphilis in Japan. Administration of intravenous penicillin G was considered as a more potent antibiotic treatment. However, as in this case, it is necessary to consider surgical resection as the treatment for uncontrolled infection and in order to exclude other diseases, including malignancy, when the lung involvement is poorly improved by antibiotics.

Lung lesions associated with syphilis are still rare, but the reported cases have been increasing as the number of patients with syphilis increases [5,6,7,8,9,10,11,12,13,14,15,16]. Thus, we should consider chest X-ray in the cases of the patients with syphilis who have pulmonary symptoms.

In conclusion, to our knowledge, this is the first surgically treated case of a lung abscess caused by syphilis, which was diagnosed by PCR techniques in TBB. This report could propose a useful diagnostic method for the pulmonary involvement of syphilis.